July 28, 2026

Dear FSHD Community:

Today, we are pleased to share that we have received clearance from the U.S. Food and Drug Administration (FDA) for our Investigational New Drug (IND) application to initiate a Phase 1 clinical trial of DYNE-302 in facioscapulohumeral muscular dystrophy (FSHD). This important milestone allows us to begin evaluating DYNE-302 in people living with FSHD. Our full press release can be found here.

We believe DYNE-302 has the potential to address the underlying cause of disease and we look forward to taking this important next step in evaluating its potential in the clinic.

DYNE-302 is designed to reduce expression of DUX4, a protein believed to be the underlying cause of FSHD. The investigational therapy leverages Dyne’s proprietary FORCE™ platform, the same technology being used in our clinical-stage programs in Duchenne muscular dystrophy and in myotonic dystrophy type 1.

Phase 1 Trial Details

We plan to evaluate DYNE-302 in a randomized, placebo-controlled, double-blind, multiple ascending dose (MAD) Phase 1 clinical trial in ambulatory adults ages 18-65 living with FSHD.

The primary objective of the study is to assess the safety and tolerability of DYNE-302.

Additional objectives of the study include understanding how DYNE-302 moves through and acts in the body, as well as measuring changes in DUX4-related biological markers in muscle and blood, including a protein in the blood called KHDC1L. These measurements may help us understand whether DYNE-302 is reaching its intended target and reducing DUX4 activity.

In the first group, 9 participants will receive three intravenous doses administered every four weeks, randomized (assigned by chance) in a 2:1 ratio of DYNE-302 1.5 mg/kg (investigational study treatment) or placebo (inactive study treatment). Following the completion of this group, Dyne intends to evaluate higher dosing and less frequent administration.

Participants who complete the placebo-controlled period may enter an open-label long-term extension portion of the trial where all participants will receive DYNE-302 for up to an additional 96 weeks.

Dyne intends to pursue a traditional approval pathway in the U.S. for DYNE-302.

Our Commitment to the FSHD Community

This milestone reflects years of scientific research and collaboration across the FSHD community. We are deeply grateful to the individuals and families living with FSHD, advocacy organizations, researchers and clinicians whose partnership has helped advance the field and make this progress possible.

At Dyne, we are committed to developing transformative therapies for people living with genetically driven neuromuscular diseases. As we take this next step with DYNE-302, we look forward to working closely with the FSHD community and sharing updates as the program advances.

Thank you for your continued support and partnership.

Sincerely,

The Dyne Therapeutics Team